1. Field of the Invention
The present invention relates generally to silicon wafer handling machines, and more particularly to systems adapted for automatically unloading silicon wafers from a Standard Mechanical InterFace ("SMIF") pod and then transferring such wafers to a process carrier, and conversely.
2. Description of the Prior Art
Certain semiconductor wafer processing operations require that a number of disk-shaped silicon wafers be loaded into a process carrier arranged in a vertical orientation. Examples of such processes are "wet bench" processing and horizontal diffusion furnace processing. Presently, silicon wafers are transported between processing tools in a SMIF pod which orients the wafers horizontally. Accordingly, in addition to transferring wafers between the SMIF pod and the process carrier, performing any wafer processing operation in which the wafers must be oriented vertically requires reorienting the wafers from their horizontal orientation in the SMIF pod into a vertical orientation in the process carrier. In addition to reorientation of wafers between the SMIF pod and the process carrier, frequently the process carrier is capable of holding more wafers than the SMIF pod. Accordingly, in general preparing wafers for a process in which they are vertically oriented requires:
1. removing a SMIF pod's wafer carrier from within the protective environment provided by the SMIF pod; PA1 2. removing the wafers from the SMIF pod's wafer carrier; PA1 3. rotating the wafers from a horizontal to a vertical orientation either while they are present in, or after they are removed from, the SMIF pod's wafer carrier; PA1 4. depositing the now vertically oriented wafers into a process carrier; and PA1 5. perhaps performing the preceding operations more than once to combine wafers from more than one SMIF pod's wafer carrier into one process carrier.
To prevent contamination of silicon wafers during processing, present semiconductor processing technology requires that all of the preceding operations be performed automatically by a machine without human intervention in the process. Thus far, automation of this wafer handling process has been achieved by cascading a general purpose SMIF pod-load interface apparatus with a wafer mass-transfer machine with a process tool, e.g. a wet bench or a horizontal diffusion furnace. Assembling an entire apparatus for either of these process tools therefore results in two mechanical interfaces, i.e. the mechanical interface between the SMIF pod-load interface apparatus and the wafer mass-transfer machine, and the mechanical interface between the wafer mass-transfer machine and the process tool. Alignment of a mechanical interface, e.g. the mechanical interface between the SMIF pod-load interface apparatus and the wafer mass-transfer machine, can be so difficult that after the two devices have been disconnected, perhaps for repair or maintenance, several hours may be required to properly realign them.
In addition to the mechanical interfaces, there also exist electrical interfaces between the SMIF pod-load interface apparatus and a wafer mass-transfer machine, and the wafer mass-transfer machine with the process tool. In particular, the electrical interfaces between each of the devices must be arranged so the combined devices operate in a coordinated manner. Interfacing the SMIF pod-load interface apparatus with the wafer mass-transfer machine has proven to be troublesome and particularly annoying for process tool manufacturers desirous of selling an integrated system which includes the SMIF pod-load interface, the wafer mass-transfer machine, and the process tool.
In addition to the difficulties associated with interfacing the SMIF pod-load interface apparatus with the wafer mass-transfer machine, the combined devices occupy more floor space than desirable, and operate comparatively slowly because they are general purpose rather than special purpose devices. For example, a standard pod load interface opens a SMIF pod and transfers the wafer carrier to the process tool. For certain processes, the wafers must also be transferred from the original carrier to a different carrier. Under such circumstances, a wafer transfer machine has to be combined with a pod load interface to translate a carrier from a position within the pod load interface to a position within the wafer mass-transfer machine. For translating the SMIF pod's wafer carrier from one location to another location, generally the pod load interface includes an arm having at least two rotary joints which merely picks up the SMIF pod's wafer carrier, translates the carrier to a new location, and then set the SMIF pod's wafer carrier down. Accordingly, if the pod load interface is to also reorient the wafers from a horizontal orientation to a vertical orientation, an end-effector must be added to the standard pod load interface for performing the prescribed rotation.
In addition, the combined SMIF pod-load interface apparatus and wafer mass-transfer machine unnecessarily replicate certain subsystems. For example, a general purpose SMIF pod-load interface and a wafer mass-transfer machine each includes an environmental control system to prevent wafer contamination. Similarly, the SMIF pod load/unload device and wafer mass-transfer machine each include a separate electronic circuit for controlling their respective operation.
In addition to a horizontal orientation for the silicon wafers within the SMIF pod, it is often desirable to arrange the wafers with the backside of one wafer facing the frontside of the immediately adjacent wafer, or conversely. Generally, the backside of a silicon wafer is more likely to be contaminated than the wafer's frontside. Therefore, during wafer processing in which the wafers retain their SMIF pod's wafer carrier arrangement, contamination of the frontside of a wafer is more likely than if the wafers were arranged backside-to-backside and frontside-to-frontside. Such a rearrangement of the wafers into the more desirable backside-to-backside and frontside-to-frontside orientation is difficult to achieve with the combined SMIF pod-load interface apparatus and wafer mass-transfer machine.